This invention relates to work-holding chucks as used on automatic turning machines.
Automatic turning machines generally utilize long bars for work feed stock which extend through the spindle of the headstock of the machine; out of the front of the spindle, and through a work-holding chuck. As a workpiece is finish-machined and cut off from the parent bar stock, the grip of the work-holding chuck can be relaxed and the bar is fed outward to present new material for machining.
Many types of bar feeder attachments are used to increment stock through the work spindle. There are pushers, which urge the work stock forward from the rear of the headstock, and there are pull type attachments which grab the part and withdraw it from the front of the chuck.
After withdrawing additional stock through the chuck for the next successive machining operations, the chuck reclamps on the work stock and, at this time, it is imperative that there be sufficient clamping stock present within the clamping area. If there is insufficient clamping stock present within the clamping area, the chuck may not be operating at its proper design forces and may tend to have overstressed points, which could operate to the detriment of the chuck assembly and cause failure of the components.
For example, if a jaw type chuck is used for clamping the work stock and there is not sufficient stock to cover the clamping face of the jaws, high unit stresses will be developed over the zone of clamp, and high bending stresses may be developed in the jaw bodies as well. Since the jaws are normally subjected to great stresses because of the flyaway tendencies of centrifugal action, the internal stresses are compounded and may cause failure of the jaws.
Prior art devices for sensing the presence of stock to allow adequate clamping have also included cumbersome mechanical devices which reach through the headstock spindle and touch the end of the workpiece which, while necessary in purpose, are impractical to use in function. Similarly, stock feelers have been contained within a chuck body which necessitates having a complex chuck unit and feedback sensing control.
The apparatus of the within invention has obviated the need for these prior art stock sensing devices by providing a self-contained stock sensing device having only mechanical features adapted to the machine, and which is capable of being readily mounted to the front face of the work-holding chuck.
It is therefore an object of the present invention to provide a mechanical unit which may be fitted to the front face of the work-holding chuck for sensing the presence of sufficient work-holding stock.
Another object of the within invention is to provide a stock sensing device which is inexpensive and easily applied.
Still another object of the within invention is to provide a stock sensing device which may be applied to jaw type work-holding chucks wherein the sensing element may be applied to the stock in a location proximate to the jaw clamping zone.